This invention is in the field of spectroscopy and spectroscopic imaging. This invention relates generally to devices and methods for obtaining infrared spectra and spectroscopic imaging data in the mid-infrared region.
The collection of spectroscopic (magnetic resonance, mass, infrared and Raman, for example) techniques that can provide imaging data are referred to as chemical imaging and are rapidly evolving for biomedical applications. Molecular spectroscopy-based imaging, including mid-infrared absorption and Raman scattering, is attractive as it can optically probe materials in a non-perturbing manner. Fourier transform IR (FT-IR) spectroscopic imaging, in particular, combines the spatial specificity of optical microscopy with the molecular selectivity of vibrational spectroscopy. Since mid-IR spectral frequencies are resonant with the fundamental vibrational mode frequencies in molecules, the IR absorption is a strong signal and the spectrum at each pixel is a quantitative “fingerprint” of composition. For example, structure in prostate tissue is manually determined after staining in current practice (FIG. 1A). For example, the biochemical content of unstained tissue has been obtained using FT-IR imaging. At each pixel in the image, a vibrational spectrum is recorded to provide a 3D data cube (FIG. 1B). By dialing-in chemistry inherent in IR spectral features (FIG. 1C), contrast similar to stains can be obtained (FIG. 1D). As opposed to human recognition, further, numerical methods can provide information objectively (FIG. 1E) as images that are color coded for cell type, pathologic status or function. Hence, chemical imaging offers the potential for recognition of the type and functional state of tissues and cells without the use of dyes, probes or human interpretation. Automation and objectivity are enabled, further, by the numerical methods needed to extract data. Chemical imaging may be contrasted with molecular imaging. While probe-based molecular imaging techniques are exceptional for monitoring specific epitopes, dyes and reagents are required and functional state of cells and tissues is limited to known pathways that involve the probe target. Chemical imaging, in contrast, requires no probes but uses computation to extract information. While the functional state can be extensively probed and multiple phenomena in multiple cell types can be monitored at the same time, the information is not as specific as that with molecular probes. The flexibility and general applicability, hence, of chemical imaging is very high but is traded-off against information detail—making it suitable for many applications. Among spectroscopic techniques, IR and Raman spectroscopy are attractive in that they can easily harness the power of optics and microscopy while providing richer molecular detail compared to the near-infrared (NIR), visible or ultraviolet regions. The Raman effect is ideally suited for analyzing wet biological materials but, unfortunately, is too weak to provide dynamic details sensitively for large numbers of cells. Non-linear and surface enhanced Raman spectroscopic methods are emerging to greatly improve sensitivity. The new methods are limited by spectral coverage and understanding the molecular/optical origin of signals in the former while may only be surface sensitive or require probes in the latter. At the same time, it is widely believed that IR spectroscopy cannot be easily conducted in aqueous environments. In summary, the exciting potential of chemical imaging is limited by technology. Hence, vigorous attempts are being made to improve instrumentation/technology in Raman and FT-IR spectroscopic imaging.
For example, International Patent Application Publication No. WO 2009/050437 discloses a system and method for infrared imaging and use of a broadband infrared source with one or more high efficiency infrared band-pass filters. Additionally, U.S. Pat. No. 6,784,428 discloses an apparatus and method for non-interferometric IR spectroscopy using an optically dispersive element.